Moistureproof gelatine



Patented Dec. 29, 1936 UNITED STATES PATENT. OFFICE mesne assignments,to E. I.

du Pont do Nomours 8; Company, Wilmington, DeL, a corporation ofDelaware No Drawing. Application August 9, 1928, Serial No. 298,634

1 Claim.

This invention relates to moistureproof articles of manufacture and moreespecially to a method of making a moistureproof gelatine film or sheet.By the term moistureproof I mean the ability to resist the transmissionor diffusion of water vapor to an extent at least as great as orexceeding that displayed by ordinary waxed papers employed as wrappersand functioning to resist the penetration of water vapor therethrough toa substantial degree for a substantial period of time. depending on thearticle being wrapped and/or being approximately '7 times or more aseffective as uncoated sheets or films of gelatine when tested inaccordance with the test set forth in the Journal of Industrial andEngineering Chemistry on page 575, vol. 21, No. 6 (June 1929) Today itis the practice to wrap various articles, such as cakes, cookies,cigars, candies, drugs, and the like in moistureproof materials. It isessential that these wrapping materials be transparent, flexible,non-tacky, odorless, and, of course, moistureproof.

I have found that I can produce a transparent, flexible, odorless,moistureproof material by coating a sheet or film of gelatine,preferably hardened, with a composition capable of rendering thegelatine moistureproof.

It is, therefore, the object of this invention to prepare a transparent,moistureproof material capable of being used as a wrapping material.

Another object of this invention is to provide a method of making amoistureproof material having gelatine as a base'and being thin,flexible, colorless, odorless, non-tacky and preferably alsotransparent.

A specific object of this invention is to provide a method of preparinga moistureproof material comprising a sheet or film of gelatine coatedwith a composition comprising a cellulose derivative and a wax.

Further objects will appear from the following description and appendedclaim.

In carrying out my invention I coat a sheet or film of gelatine,preferably hardened by any of the Well-known hardening agents, such astannins, potassum bi-chromate, formaldehyde, and the like, with asuitable moistureproofing solution. Preferably, the solution which I usecomprises a cellulose derivative, a wax, a plasticizer, a gum and asolvent or solvent mixture. After the application of the coatingcomposition to the base, which may be by spraying, immersion or othermanner to one or both sides of the base, the solvent mixture is removedby subjecting thetreated material to a drying or heated atmosphere,

This step is best carried out at a temperature approximately that of themelting point of the wax used in the coating solution for the reasonthat separation of the wax and, therefore, "blushing is prevented.

The drying step may render the coated sheets somewhat brittle. If thisis the case, the coated sheets may be subjected to an atmosphere,wherein the coated sheets are humidified and whereby the flexibility ofthe product is restored. This step is also preferably carried out at atemperature approximately that of the melting point of the wax in thecoating composition. The flexibility of the final product may be partlycontrolled by' incorporating in the gelatine composition forming thesheet or film, any of the well-known softening agents for gelatine.

A gelatine film or sheet coated in this manner produces a satisfactorymoistureproof material in which the adhesion of the coating to the baseis satisfactory. However, if desired, the adhesion of the coating to thebase may be increased by hydrolyzing the surfaces of the gelatine filmor sheet prior to coating.

When the coating composition is applied to gelatine having hydrolyzedsurfaces the solvent in the coating composition tends to partiallydissolve the layer of hydrolyzed gelatine, thereby anchoring thesuper-imposed coating to the base of gelatine. The hydrolysis may ducedinvarious ways. I have found that when the geiatine film is subjected toa 1-2% acetic acid solution at a temperature of between -90 C. for arelatively short period of time, about one to ten minutes, satisfactoryresults are obtained.

The composition may be applied to one or both sides of the gelatine baseto form, when dry, coatings ranging from .00005 to .0005 of an inch in.thickness. The thickness of the final product will depend largely onthe thickness of the gelatine base and whether or not both surfaces ofthe base are coated. Thus the thickness of the final product may varyfrom .0005 to .01 of an inch or even greater.

The composition which I employ as my moistureproofing solution, aspreviously stated, comprises a cellulose derivative, a wax, gum orresin, a plasticizer and a solvent or solvent mixture. The cellulosederivative which may be used may be nitro-cellulose, cellulose acetate,cellulose ether and the lil.e.

The gum or resin that I may use may be estergum, resin, gum-mastic,copal resins or synthetic resins. These gums or resins may be usedeither singularly or in combination.

be obtained and prowhen tri-cresyl phosphate, tri-phenyl phosphate,

di-amyl phthalate or di-butyl phthalate, or castor oil were used.

The above ingredients when used in proper proportions and with suitablesolvents produce a material which, after evaporation of the solvent, isnot only moistureproof, but is flexible without cracking, perfectlytransparent, devoid of greasiness or tackiness and has the requisitetensile strength for the purposes for which it is desired to be used.Various proportions of the above ingredients may be used. I have foundthat satisfactory results may be obtained when the ingredients are usedin the following percentages, by weight:

- Percent Cellulose derivative -70 Gum--- 30-60 Wax 2-6 Plasticizer,5-30 v plasticizer and cellulose derivative.

The following specific examples have produced satisfactory results:

The wax and cellulose derivative base ordinarily' do not mix to form aclear film. However, by a proper choice of gum it has been foundpossible to make the combined gum and wax mix with the mixture is thenchosen to retain the gum, wax, cellulose derivative and plasticizer intheir proper proportions in complete solution until the entire solventis evaporated. g

It is desirable to employ solvents for the waxes a,oes,ves

The solvent up to 50% or over, byrweight, in orderio maintain the wax insolution during the process of drying the coating to employ relativelylow percentages of intermediate boiling solvents for thenitro-celluiose. By employing these solvents in a proportion of 10% andunder of the total solvent a too rapid drying of the coating 7 larsolvent must be determined separately for the particular composition, Ihave found that the following specific solvent combinations when usedwith the respective examples of compositions above described, producesatisfactory results:

Solvent for Example 1:

Percent based on total volume of solvent Alcohol---; 25 Ether- 43Toluene 18 Butyl acetate 14 Solvent for Example II:

Ethylacetate 62 Toluene 27 Alcohol 9 Butyl acetate 2 In this applicationI make no claim to the particular coating composition, since it isclaimed in the co-pending application of Charch and Prindle, Serial No.308,873 died Sept. 27, 1928.

Though the moistureproof geiatine has been described as particularlyadapted as a wrapping material this invention is in nowise limitedthereto, since various other uses will become apparent to one skilled inthe art.

I claim:

In a method of making a transparent, flexible, non-tacky andmoistureproof sheet material suitable for use as a wrapping tissuewherein the moistureproof coating effectively adheres and is secured tothe base, the steps which comprise treating the surface of a film ofgelatine with an aqueous solution containing 1 to 2% of acetic acid at atemperature of approximately between 50 to 90 C. for approximately 1 to10 minutes to form a hydrolyzed gelatine surface to which 9.moistureproof composition will effectively adhere, and thereafterapplying to the hydrolyzed surface a moistureproofing compositioncomprising a cellulose derivative and a wax in proportions to produce atransparent, flexible, adhering, non-tacky and moistureproof coating,whereby a moistureproof coating is eflectively secured to the gelatinebase sheet or film.

WILLIAM HALE (EH-ARCH.

or sheet. Also, it is desirable is prevented. While'the particu-'

